Electrical contact member



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lliiay 9 inghouse Electric & Manufacturing @ornpany, East Pittsburgh, lPa., a. corporation of Pennsylvanla No Drawing. application September ltd, 1938, fits-rial No. $29,866

"This invention relates to electrical make and breast contact members.

Contact members of refractory metal powders and a metal having good conductivity such as copper or silver have been employed heretofore. Recently carbon has been so added to the composition of the contact members that when heat treated it will combine with the refractory metal and form a refractory carbide, thereby increasing the hardness of the contact member. Such refractory carbide is undesirable since it increases the resistivity of the metal and lowers the melting point of the refractory with which it combines.

an object of this invention is to provide a contact member having high physical properties, wear characteristics and good conductivity.

Another object of this invention is to provide a composite contact member formed from refractory metal powders and an alloy of copper cobalt and iron.

it. further object of this invention is to provide a contact member formed from refractory metal powders and an alloy which is susceptible to an age hardening heat treatment to give high physical properties and good conductivity to the contact member.

Other objects of this invention will become apparent from the following description and the [l ap ended claims.

in practicing the present invention, a contact member is formed from a plurality of metals which have been found to cooperate to give certain desired characteristics. A base body of refractory metal selected from the group tungsten, molybdenum and tantalum and which has a rela ivelv high melting point so formed as to have i terstices therein and which of itself does not ossess the des red characteristics is impregnated wi h a cooper base alloy of lower melting point as will be disclosed more fully hereinafter to give a esulting product having the desired characteristics.

in forming the metal base here employed, re-

' fractory metal powders of a predetermined size F base is to mix the refractory metal powders of (m. Nil-166i predetermined size with suiilcient organic bond to form a: plastic putty-like mass which is moldable or which may be rolled and cast to a dc sired shape. Any suitable organic bond which can be removed by drying or sintering the shaped mass to leave a porous structure may be em-- ployed. It is highly desirable to employ a bond which can be substantially completely removed so as not to leave a carbon residue which may combine with the refractory metal in the form of a carbide since such carbides are undesirable. An organic bond composed of about 75% of shellac and 25% of alcohol is entirely satisfactory in forming the putty-like mass, and when the mass is heated at a temperature of about 1000" in reducing atmosphere, is substantially completely removed leaving the desired porous base of ra fractory metal.

In order to impart the desired electrical chow acteristics to the contact member, the porous refractory metal base or slug is then filled with the impregnating alloy. The alloy employed in the contact member of this invention is a copper base alloy which contains cobalt and iron as es sential elements therein in predetermined proc portions as disclosed and claimed in James its. Kellys copending application Serial No. i ,l filed June 19, 1937, now Patent directed to Copper base alloys.

in the impregnating alloy, the cobalt are each present in amounts ranging from a s but effective amount up to 5% with the balance substantially all copper. As disclosed in the hereinbefore identified Kelly Patent, a preferred range of each of the cobalt and iron contents. is between 5% to 3% while the best combination of properties obtained where the ratio of the cobalt to iron in the alloy is between .5 to l with a preferred ratio of l to 1. These all rs are susceptible to age hardening and when treated as by quenching them from a temperature of between 750 (3. and 1075 C. and aged at a temperature between 450 C. and 680 (3. have electrical conductivity of 60% or greater, and a hardness approximating 80 Rockwell or greater.

When the sing or body of the contact member is so formed from the refractory metal powders in either of the ways described hereinbefore as to have a predetermined porosity, it is imprcgnated with the copper-cobalt-iron alloy. in practies the refractory metal powders may be so formed that the body will comprise from 50% to 90% of the finished contact member, the balance being the copper base alloy having the cobalt and iron present in the quantities and ratios indicated hereinbefore. With the organic bond method of making the refractory metal body, it is possible to secure a more uniform and more porous body, so that when it is desired to employ an alloy content of from' 30% to 40% in the contact member the organic bond method of forming the refractory metal body is preferably utilized.

In order to impregnate the refractory metal body or base of the contact member, the preformed base is placed in a suitable furnace in a refractory container in the presence of a definite amount of. the copper-cobalt-iron alloy and subp} jected to heat at a temperature above the melting point of the alloy, but below the melting point of the refractory metal in a reducing atmosphere. At this temperature the alloy melts, wets and impregnates the porous refractory base securely bonding to the refractory to form a strong homogeneous article when cooled.

For general applications, contact members of from 80% to 55% of the refractory metal powders impregnated with from 20% to 45% of the copper base alloy having a cobalt content of from .5% to 3% and an iron content if from .5% to 3% and in which the cobalt to iron ratio is between .5 and 1.25 to 1 are satisfactory.

Where the organic bond method is employed in making the refractory metal base, it is found that the resulting impregnated contact member responds to a heat treatment as described hereinbefore for effecting the age hardening of the copper base alloy in the contact member to improve the physical and electrical characteristics of the contact member over those characteristics obtained in the unheat treated contact members. However, when the refractory metal base is formed by the pressure method, it is found that a heat treatment to age harden the impregnating alloy is not always necessary unless it is desired to improve the conductivity, since the copper base alloy particles in the contact member are so small that hardening them has substantially no eifect on increasing the hardness of the contact member as a unit. Even without the heat treatment the hardness values obtained in contact members formed under the high pressure method are as a general rule somewhat higher than those obtained in the contact members formed by the organic bond method. In both cases the contact members produced have excellent physical and electrical properties.

Contact members of the refractory metal tungsten impregnated with the copper-cobalt-iron alloy and which are representative of the contact members comprising this invention are as follows:

N Percent Percent Percent Percent W u on Fe In making the contact member No. 10, the tungsten powders of 200 mesh size were compacted into the predetermined shape of the base of the contact member under tons cated hereinbefore increases the hardness and conductivity of the contact members over the values obtained in the untreated contact members formed by the organic bond method and improves the conductivity of the contact members formed by the pressure method.

Under test conditions, the contact members of this invention consistently have a life of more than 119,000 operations or interruptions when employed as the contact membersin an oil circuit breaker connected in a three-phase circuit and operated under rated conditions of 60 amperes, 440 volts at 60 cycles, with reactors connected in the circuit to serve as the load and to provide a low power factor. In the test the breaker was tripped at the rate of '27 times per minute for" measuring the life of the contact members.

By practicing this invention, contact members are produced having an extremely high hardness and good conductivity which are free from the carbon contamination employed heretofore for improving the wear characteristics of the contact members. The alloy employed in the contact members imparts the desired characteristics, both physical and electrical, which are desired in the contact member, providing a contact member having wear resistance, low resistivity and good conductivity. Further such contact members can be brazed to the contactor arm to give a good rigid electrical connection without detri- .mentally affecting the physical and electrical characteristics of the contact member.

Since certain changes may be made in the processes described hereinbefore, and certain modiflcations may be made in the resulting disclosed contact member which embodies the invention without departing from its scope, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense. This invention is therefore not to be limited except insofar as is necessary in accordance with the teachings of the prior art and the scope of the appended claims.

I claim as my invention:

1. An electrical contact member comprising a body portion of refractory metal powders bonded together with an alloy comprising from .5% to 5% of cobalt, from .5% to 5% ,of iron with the balance substantially all copper.

2. An electrical contact member comprising from about 90% to 50% of refractory metal powders and from about 10% to 50% of a copper, cobalt and iron alloy, the alloy comprising from .5% to 5% of cobalt and from .5% to 5% of iron with the balance substantially all copper.

3. An electrical contact member comprising from to 50% of refractory metal powders impregnated and integrally united with from 20%, to 50% of an alloy composed of from .5% to 3% of cobalt, from .5% to 3% of iron with the balance copper.

4. An electrical contact member comprising from 80% to 50% of refractory metal powders impregnated and integrally united with from 20% to 50% of an alloy composed of from .5% to 3% of cobalt, from .5% to 3% of iron with the balance copper, the impregnated refractory metal being heat treated to give high physical strength and conductivity to the alloy.

5. An electrical contact member comprising from 80% to 55% of tungsten powders formed to a predetermined shape and impregnated with from 20% to 45% of an alloy composed of from .5% to 3% of cobalt, .5% to 3% of iron with the balance copper and in which the ratio of the 8. An electrical contact member comprising about 60.5% of tungsten, about 37.7% of copper, about .85% of cobalt and about 1% of iron, the copper, cobalt and iron being in the form of an alloy bonding the tungsten powders.

9. An electrical contact member composed of about 60% by weight of tungsten and 40% by weight of an alloy having the analysis of 1.45% of iron and 1.20% of cobalt with the balance copper.

JAMES M. KELLY. 

